The present invention relates generally to elastomer energized seals for use in high pressure applications. More praticularly, the present invention relates to an improved back-up ring assembly for use with such elastomer energized seals to prevent deformation and extrusion of the cap seal of the seal assembly during operation at high pressures.
Elastomer energized seals are commonly used to provide a seal between various mating surfaces found in a wide variety of mechanical devices. Elastomer energized seals are used widely in hydraulic devices such as landing gear struts, hydraulic power tools, hydraulic actuators and a wide variety of other mechanical devices including internal combustion engines, vacuum pumps, etc.
The most common type of elastomer energized seal is the O-ring type seal which is used in piston or rod sealing applications to provide a seal between two adjacent cylindrical surfaces. The elastomer energized seal is mounted within a groove in one of the surfaces and extends annularly across the gap between the two surfaces for sealing against the other surface. The elastomer energized seal is a two piece seal which typically includes a plastic cap seal or sealing ring which is energized against the mating or sealing surface by an elastomer expander ring. Expander rings are usually made from an elastic material such as rubber or synthetic equivalents having elastic properties similar to rubber. The cap seal is typically made from a low surface tension plastic such as polytetrafluoroethylene (PTFE) or soft metal.
During high pressure applications, i.e., 3,000 pounds per square inch gage and over, the cap seal of the seal assembly tends to deform and become gradually extruded into a gap between the adjacent surfaces. This gap is commonly known as the extrusion gap. Problems with extrusion of the gap seal are particularly severe during high pressure or vacuum applications. This is especially troublesome when reciprocating surfaces are being sealed for piston-cylinder or rod-bore sealing systems.
In order to prevent or at least reduce extrusion of the cap seal into the extrusion gap, various back-up or anti-extrusion rings have been developed which are positioned on either side of the elastomer energized seal assembly. The back-up rings are typically one piece rings which are made from a relatively hard material having a high modulus of elasticity. The back-up rings have conventionally been designed to abut against both the cap seal ring and the elastomer energizer ring.
Although back-up rings made from relatively hard materials are effective in preventing extrusion of the cap seal into the extrusion gap, problems have been experienced with the elastomer energizer being abraded or chafed by contact with the back-up ring. The use of softer back-up ring materials in order to reduce chafing of the elastomer energizer is not possible because the softer materials are not effective in preventing extrusion of the cap seal.
It would be desirable to provide a back-up ring which provides adequate protection against cap seal extrusion at high pressures or high vacuums, while providing protection for the elastomer energizer ring against abrasion.